The present invention relates to a surface inspection apparatus for inspecting a surface state of an object and more specifically to a surface inspection apparatus most suitable as a wafer surface inspection apparatus for inspecting a foreign substance, flaw or the like on a surface of a semiconductor wafer.
In general, a semiconductor integrated circuit is manufactured by forming a circuit on a semiconductor substrate (wafer) by photolithography process. In this case, a number of the same integrated circuits are formed on one sheet of wafer, and finally these circuits are separated into a number of single semiconductor integrated circuit chips. Then if a foreign substance exists on the wafer, a defect is produced in a circuit pattern formed on the part and the integrated circuit becomes unable to be used. As a result, the number of integrated circuits obtained from one sheet of substrate is decreased and the yield is lowered.
Such a foreign substance seems to adhere in CVD process where a metal film is formed on a wafer surface. That is, a foreign substance produced within a process apparatus adheres to a wafer leaving the apparatus, and becomes a defect in the lithography process afterward subjected to.
Therefore in the field of the semiconductor integrated circuit manufacturing, a wafer for inspection called a monitor wafer is used, and monitoring of generation of a foreign substance is performed. The wafer for inspection passes through the process apparatus in a similar manner to a material wafer, and the monitor wafer is inspected before or after the operation and if generation of a foreign substance is recognized, measures such as cleaning of the apparatus are taken.
As an inspection method, in general, laser beams are converged on a wafer surface and scattered lights from the converging point are received and a foreign substance or the like is detected from signals of the received lights.
FIG. 32 shows an example of a wafer surface inspection apparatus in the prior art.
A laser is used for a light source 121. Lights going out of the laser beam source 121 are converged on a surface of a wafer 101 by an optical system 125. The converged laser beams are scanned in one direction using a light deflector 123, a motor 126 or the like and a scan line SL is formed. At the same time, the wafer 101 is moved in direction orthogonal to the scan direction by a moving unit 110. As a result, the whole surface of the wafer 101 is scanned by the laser beams. The scattered lights from the converging point on the wafer 101 are received through a collector lens 127 of a light receiving unit 130 by a photoelectric converter 131. The photoelectric converter 131 receiving the scattered lights outputs signals of a pulse shape in response to the intensity of the scattered lights when the converging point crosses a foreign substance or the like. The size of the scattered object is decided depending on the amount of the signal output.
When the whole surface of the wafer is inspected by the laser beams, a scan range slightly wider than the wafer must be scanned. Because when the luminous flux is returned, there is a moment becoming the stationary state, and in general, in this point, a pulse signal can not be obtained and the inspection can not be performed.
However, when the scan range is set slightly wider than the wafer, following inconvenience is produced when lights strike an edge portion of the wafer.
That is, in the wafer surface inspection apparatus, a photoelectric converter of high sensitivity is used in order to detect weak scattered lights due to a foreign substance on the wafer. On the contrary, since the scattered lights produced at the edge of the wafer is significantly large in comparison with the scattered lights due to the foreign substance, the photoelectric converter does not act normally for a while after receiving the scattered lights produced at the edge of the wafer. Since the converging point is continued to be moved during this state, some range from the edge of the wafer can not be measured.
For example, when the beam is subjected to a raster scan and the measurement is performed at the scan state in one direction, a region incapable of being inspected is produced as shown in hatching in FIG. 33. The dimensions of this region become large as the scan speed of the beam becomes rapid. Consequently if the wafer becoming larger in diameter is to be inspected in a short time, the region incapable of being inspected becomes large and the exact inspection can not be performed.